I am confused about how I use curse when a chest is opened, since all of my cards seem to be 'triggered' by actions instead of curses.

When a chest is opened, the Overlord player receives 1 threat per player for each curse in the chest. As detailed in the FAQ, threat gained from these curses can be used to play a Trap (Chest) card on the chest that was just opened. Doing so might delay the distribution of everything else in the chest (except the curses.) For example, using the curses from the chest to play a Mimic trap card. The heores would then need to kill the mimic before they saw any of the actual treasure.

Thank you. I thought there were cards unique to curses. I missed the part about earning threat from them.